1. Field of the Invention
This invention relates to a process for the production of an acoustic treatment panel that integrates the function of frost treatment with hot air, whereby said panel is designed in particular for a leading edge of an aircraft, and more particularly for an air intake of an aircraft nacelle.
2. Description of the Related Art
Such a panel is described in particular in the patent FR-2,917,067. It comprises—from the outside to the inside—an acoustically resistive layer, at least one alveolar structure, and a reflective layer, as well as channels that are each bordered by a wall that is inserted between the acoustically resistive layer and the alveolar structure.
This solution makes it possible to limit the risks of communication between the inside of the channels and the cells of the alveolar structure and therefore the risks of disruptions of acoustic treatment.
According to another advantage, the hot air occupies a volume that is considerably smaller relative to the prior solutions, according to which it occupies the volume of certain cells of the alveolar structure, which makes it possible to produce, on the one hand, a better concentration of hot air against the wall to be defrosted, reinforcing the effectiveness of defrosting, and, on the other hand, a higher pneumatic pressure that limits the risk of the pressure inside the structure being lower than that of the outside and therefore the penetration of the outside air inside the defrosting system.
According to another advantage, the hot air is in permanent contact with the skin to be defrosted, which makes it possible to improve the exchanges and to reduce the temperature of the hot air that is delivered at the outlet of the defrosting system; this makes it possible to discharge the air without the risk of the wall that it passes through being burned, in particular when this wall is made of a heat-sensitive material such as a composite.
According to a first embodiment that is described in the patent FR-2,917,067, the acoustically resistive layer comes in the form of a first piece of sheet metal. To form the channels, a second piece of sheet metal is shaped in such a way as to produce furrows, and then it is flattened and made integral with the inside surface of the first piece of sheet metal. Next, perforations are made in the two pieces of sheet metal in the areas where they are in contact. In parallel, a first surface of the alveolar structure is made integral with the reflective layer. The other surface of the alveolar structure is cut out in such a way as to form—at said surface—shapes that are complementary to those of the channels. Next, the alveolar structure is made integral with the second layer that borders the channels.
This operating mode makes it possible to simplify the assembly mode because the walls that border all of the channels are connected to one another and originate from the shaping of a single piece of sheet metal.
However, the superposition of two pieces of sheet metal at the perforations leads to having perforations with relatively long lengths, which impacts the operation of the acoustic treatment and makes it less efficient.
According to another drawback, it is difficult to obtain satisfactory sealing between the pipes of the alveolar structure that empty out facing the channels because it is relatively difficult to weld the ends of the pipes with a surface that is not flat and has a complex shape.
According to another operating mode that is described in the patent FR-2,917,067, each channel comes in the form of a strip of shaped material. According to this variant, the strips of material that border the channels are flattened and individually made integral with the inside surface of the first piece of sheet metal.
To ensure the passage of sound waves, the acoustically resistive layer can comprise a cloth that may or may not be metal, such as a wire mesh, and at least one structural layer, for example, sheet metal or a composite with oblong holes or microperforations.
In parallel, a first surface of the alveolar structure is made integral with the reflective layer. The other surface of the alveolar structure is cut out in such a way as to form—at said surface—shapes that are complementary to those of the channels. Next, the alveolar structure is made integral with the second layer that borders the channels.
This operating mode does not impact the operation of the acoustic treatment to the extent that the strips used for forming the channels separate the acoustically resistive layer in the areas that are provided for the acoustic treatment.
However, the installation of the material strips that border the channels on the acoustically resistive layer takes a relatively long time to carry out, especially since the connection between the edges of the strips and the acoustically resistive layer is to be airtight so as not to disrupt the acoustic and/or frost treatments.
According to another drawback, as above, it is difficult to obtain satisfactory sealing between the pipes of the alveolar structure that empty out facing the channels because it is relatively difficult to weld the ends of the pipes with a surface that is not flat and that has a complex shape.